I. Field of the Invention
This invention relates generally to a high resolution display monitor interface and related interfacing method, and more specifically to an interface and related interfacing method for communicating updated image information from a source of that image information to a monitor input terminal of a high resolution monitor.
II. Background Information
A high resolution monitor interface typically includes a data buffer, a refresh memory, a monitor input terminal, a bus linking the data buffer and the refresh memory, and a bus linking the refresh memory and the monitor input terminal. The data buffer and refresh memory both store information indicative of images to be displayed on a monitor at particular discrete display locations of the monitor. The data buffer stores selective new image information. The refresh memory stores a complete set of image information. The existence of new image information for the data buffer indicates that the image presently being displayed on the monitor from image information stored in the refresh memory requires updating.
The new image information is retained by the data buffer until this new image information can be transferred to the refresh memory. In a typical system, only at specific time periods is the refresh memory available to receive new image information from the data buffer. The refresh memory is available to receive new image information only when not being used to refresh the monitor image.
The refresh memory stores digital image information for every discrete display location of the monitor. The monitor, which retains an image for only a finite period of time, uses the image information stored in the refresh memory and periodically transferred to the monitor input terminal, to retrace the monitor image. The monitor image is presented in lines of picture elements or pixels. The monitor has an electron beam which is modulated by image information supplied to the monitor input terminal to scan and thereby refresh each pixel across a line. After completion of a line scan, the electron beam returns to the beginning of a subsequent scan line to begin refreshing each pixel in that subsequent line. After completion of the last line of each scan, the electron beam returns to the top of the scan. The time taken for the electron beam to return to the beginning of a subsequent line from the last pixel of the previous line (horizontal "flyback") or to the top of the scan after completion of the last scan line (vertical "flyback") is very short. In that brief time, the refresh memory is not being used to refresh the monitor, that is, to transfer image information to the monitor input terminal, and is available then to receive new image information from the data buffer.
While the electron beam is returning to begin another line, that is, in the periods referred to as horizontal or vertical "flyback", the data buffer which is connected by a bus to the refresh memory is enabled to read the new image information stored in the data buffer to the refresh memory, and the refresh memory is correspondingly enabled to write the new image information from the data buffer into the refresh memory.
If the monitor is a high resolution monitor, the amount of image information required to update any part of the monitor image may be quite large and the flyback periods quite small. In the brief time of "flyback" when the data buffer is enabled to read and the refresh memory is enabled to write, as much of the new image information as time permits is transferred to the refresh memory. More information can be transferred to the refresh memory if the data buffer and the refresh memory have high bandwidths, that is, can write and read many parallel bits of information simultaneously. If the bandwidth is low, not much information is passed during "flyback". Even if the bandwidth is high, because the new image information can only be passed to the refresh memory during "flyback" the amount of information that can be passed is severely limited. Hence, very many flyback periods are required to transfer significant amounts of new image information. As a consequence, the new image is "painted" on the monitor.
Another method of updating the monitor is to disrupt the scanning processes and transfer new image data to the refresh memory buffer in one burst. The effect of this process is to interrupt the viewed image and cause a visual flicker.
Thus, the present form of interfacing makes difficult any solution to the above-described problems of slow painted or flickered updating of the monitor image. The dilemma set forth above becomes more acute with high resolution interfaces which need to transfer more image information than do typical interfaces in order to fully update a monitor image.
Accordingly, an object of the present invention is to provide a monitor interface and related method having a refresh memory which may more effectively receive new image information from a data buffer than in prior systems.
An additional object is to provide an interface and related method which can achieve "flickerless" update at monitor frame rates.
A still further object of the present invention is to provide an improved interface and related method for a high resolution monitor.
Additional objects add advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention.